1. Field of the Invention
The present invention relates to pressure sensors for detecting a pressure of a fluid and/or a gaseous medium.
2. Description of Related Art
Pressure sensors of the above-noted type are known from a variety of applications. Reference is made below, in particular, to applications in automotive engineering, for example pressure cells for intake manifold or boost pressures, brake pressures, air spring pressures, tire pressures, hydraulic reservoir pressures, shock absorber pressures, coolant pressures, modulation pressures in automatic transmissions, brake pressures, fuel tank pressures, or combustion chamber pressures. Reference is made, in particular, to applications in fuel tank pressure sensors for motor vehicles. In principle, however, other automotive or non-automotive applications are also possible. For possible pressure sensors in automotive engineering, reference may be made to Robert Bosch GmbH: “Sensoren im Kraftfahrzeug” (Sensors in Motor Vehicles), 2007 edition, pp. 74-76 and pp. 128-130. The pressure sensors described therein are also modifiable according to the present invention and may be equipped with a pressure compensation unit according to the present invention.
In many pressure sensors, in particular differential pressure sensors, a pressure difference is measured between a measuring chamber which is connected to a sensor element of the pressure sensor, directly or via a measured pressure supply means, and a reference pressure chamber. In pressure sensors of this type, a so-called pressure compensation unit is frequently required which is intended to compensate a pressure difference between the reference pressure chamber and the environment. In many fuel tank pressure sensors, for example, a fuel tank pressure is supplied to the back of a silicon diaphragm from below, while a pressure present in the environment acts upon the front of the silicon diaphragm from above, for example through an opening in a sensor housing. However, to protect the front of the silicon diaphragm against environmental influences such as water and/or contaminants, the pressure compensation unit has a gas-permeable filter diaphragm which is built into a reference pressure opening. This filter diaphragm of a gas-permeable design is used as a pressure compensation element, is ordinarily designed to be water-repellent and impermeable to fluids, and is used to seal the reference pressure opening of the fuel tank pressure sensor of the built-in fuel tank unit, for example against fluids. This approach is intended to prevent spray water, for example, as well as other fluid or solid media, from entering the reference pressure chamber, regardless of the installation position of the pressure compensation element. An example of a pressure compensation unit of this type is described in the published German Patent Application DE 10 2008 004 358. This publication describes a pressure compensation unit having a housing cover and a gas-permeable filter diaphragm which covers an air opening. The pressure compensation unit includes a cap-shaped cover element which covers the filter diaphragm.
A technical challenge of known pressure compensation units is the fact that pressure compensation units require a large installation space. However, it is not possible to reduce the size in many cases, since size reductions may cause capillary effects to occur in the openings of the pressure compensation unit, through which liquids and/or contaminants, in turn, may collect in and adhere to the pressure compensation unit, which might impair the functionality.